The present invention relates generally to an optical media detector and in particular to a note detector for use in an Automated Teller Machine.
A detector in accordance with the present invention has application, for example, to the detection of skewed bank noted in the transport path of an Automated Teller Machine (ATM). In the cash dispensing mechanism of the aforementioned ATM it is important to provide a simple and reliable means for detecting skewed notes. Notes can become skewed as they are transported from a note storage cassette to the output slot of the ATM, as can notes deposited by a user and it is equally important to detect skew in notes being deposited in the ATM.
A variety of different prior art detectors have been utilized to detect note skew in ATMs. These include both electromechanical and optical detectors. However, they all have certain features in common. In particular, they all rely on a pair of sensors, each of which is located at a predetermined position along the transport path within the ATM. Also as the detector is arranged to determine skew perpendicular to the direction of travel along the transport path, both the sensors and light sources must be located within the transport path, thus making assembly and serviceability of the detectors difficult. For example, cables must be laid into both sides of the transport path to connect to the sensors.
In addition, bank notes, particularly street quality bank notes can be wrinkled and/or overlapped to some degree. When more than one such note is superimposed, the physical contact between the surfaces of the notes is unpredictable. A reduction in the intensity of transmitted light has been observed in areas where contact has been lost. Additionally, the exact position of the note within the air gap between planar light guides has been seen to affect the intensity of the transmitted light. The light beams spread as they travel between the top and the bottom light guides which reduces the light intensity falling in the receiving guide. The larger the size of the air gap between planar light guides the larger the light intensity loss.